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Re: Best Secondary Surface coating
From: Vivian[SMTP:V.C.Watts-at-btinternet-dot-com]
Reply To: Vivian
Sent: Thursday, November 20, 1997 1:26 PM
To: Tesla List
Subject: Re: Best Secondary Surface coating
Hi All,
Thanks for the response on the best surface coatings. I have been doing a
little research. The Epoxy Resin I was using was designed for potting
electrical circuits. But I didn't know the ratio's of coating to hardener
(I had acquired it as it was past if shelf date). I used 1:1. I have now
found it should have been 3:1 (so too much hardener).
I have examined the surface of the failed secondary under a microscope and
can see numerous small bubbles. The trouble is I don't know if they were
their before I fired it up. The appearance did change with time becoming a
little more milky but upon closer examination these are just bubbles. No
evidence or arcing or where the shorted turns are though. Its surprising on
closer inspection how much of a gap their is in what I thought was close
wound. Calculations show I was packing at 95%.
The dielectric constant of the stuff I used was around 12Kv/mm. From what I
can find Polyurethane is also around this figure. The best it would seem is
conformal coatings at 90Kv/mm which beats anti Corona Lacquer at 48Kv/mm.
Jeff Parisse info from the list "Red 601" insulating varnish translated to
84Kv/mm.
My original secondary was 4.25" * 20" close wound. My new one is 6.25" *
23.5" double space. It will give a little more inductance. I have coated
it with Insulating Varnish but it needs a lot more. Question is I have run
out of varnish but I do have a lot of this Epoxy resin left. Mmm Maybe I'll
sleep on it.
Viv Watts UK.